When during an industrial process using a heat exchanger with brazed plates, it is necessary to cause a fluid to circulate over only a portion of the length of the exchanger, and when it is necessary that the process does not involve the circulation of another fluid over the complementary temperature range of the exchanger, one is confronted with the following choice: either one accepts that the complementary portion of the length of the corresponding passages constitutes a thermally inactive space in the exchanger, which decreases the overall performance, or one circulates in this spacer another fluid, which one returns to a smaller flow section within the range of temperatures affected by the fluid. This second solution is more satisfactory from the thermal point of view, but in the present art, it involves substantial complication of the structure of the exchanger with particularly the addition of numerous lateral boxes for the inlet/outlet of fluids.
The invention has for its object to permit choosing the second solution above, but with less cost.